Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. For example, one network may be a wireless local area network (WLAN) in accordance with the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard (e.g., Wi-Fi) or a wireless personal area network (WPAN) in accordance with the IEEE 802.15 standard. Another example wireless network may be a 3G (the third generation of mobile phone standards and technology), 4G, or later generation system, which may provide network service via any one of various radio access technologies (RATs) including EVDO (Evolution-Data Optimized), 1×RTT (1 times Radio Transmission Technology, or simply 1×), W-CDMA (Wideband Code Division Multiple Access), UMTS-TDD (Universal Mobile Telecommunications System-Time Division Duplexing), HSPA (High Speed Packet Access), GPRS (General Packet Radio Service), or EDGE (Enhanced Data rates for Global Evolution). The 3G network is a wide area cellular telephone network that evolved to incorporate high-speed internet access and video telephony, in addition to voice calls. Furthermore, a 3G network may be more established and provide larger coverage areas than other network systems. Such multiple access networks may also include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier FDMA (SC-FDMA) networks, 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) networks, and Long Term Evolution Advanced (LTE-A) networks.
A wireless communication network may include a number of base stations that can support communication for a number of mobile stations. A mobile station (MS) may communicate with a base station (BS) via a downlink and an uplink. The downlink (or forward link) refers to the communication link from the base station to the mobile station, and the uplink (or reverse link) refers to the communication link from the mobile station to the base station. A base station may transmit data and control information on the downlink to a mobile station and/or may receive data and control information on the uplink from the mobile station. The forward and/or reverse links may be established via a single-in single-out (SISO), multiple-in single-out (MISO), or a multiple-in multiple-out (MIMO) techniques.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
Certain radio frequency (RF) front-ends of wireless communication devices (e.g., mobile stations and/or base stations employed in MIMO communications) have multiple receiver (RX) paths, multiple transmitter (TX) paths, or multiple transceiver paths, also known as chains. Each of these paths (chains) in a multipath RF front-end may have its own local oscillator (LO). The various LO signals may be generated from a single voltage-controlled oscillator (VCO) using, for example, a divide-by-2 (Div2) frequency divider associated with each LO path. Although all of the frequency dividers may output the same LO frequency, each divider in an LO path may arbitrarily start-up either in-phase (0°) or out-of-phase (180°) relative to another divider in another LO path. In order to achieve particular capabilities or perform certain functions, such as beamforming and MIMO communication, it may be desirable to operate the dividers located in different LO paths in-phase.
Accordingly, what is needed are techniques and apparatus for detecting whether two or more high frequency periodic signals are in-phase or out-of-phase and adjusting phases of out-of-phase signals.